How to compile Busybox for ESXi ... kind of Part 2

Continuing from part1 of How to compile Busybox for ESXi ... kind of Part 1 we found some challenges in compiling VMware's Busybox version found in ESXi OSS Source Code. In this article, we will go through process of compiling the latest version of Busybox which is currently 1.18.3 to run on ESXi.

Again, before getting started, a word of caution:
!!!! THIS IS NOT SUPPORTED BY VMWARE - PLEASE USE AT YOUR OWN RISK !!!! 

The build environment that I used is running the latest version of CentOS 5.5 64bit which can be downloaded here.

Download busybox-1.18.3.tar.bz2 from the Busybox's website and SCP it to your build system.

You will also need to install the following packages, you can do so using yum if you are using CentOS or RHEL and have a proper repository configured. You can use the following:

yum install -y gcc flex bison texinfo ncurses-devel libselinux-devel.x86_64 pam-devel.x86_64

Extract the contents of busybox-1.18.3.tar.bz2 using the following command:

tar -xvjpf busybox-1.18.3.tar.bz2

You will now change into the busybox-1.18.3 directory and from here you have a few ways of building Busybox. To get a list of build options, use the following command:
make help

You can customize the build of Busybox by enabling and disable specific applets to be compiled. If you want to build Busybox with no applets (not really useful), you can run the following command:

make allnoconfig
make

Once the compilation is complete, you will now have a Busybox binary in which you can run but it does nothing useful:

You can also perform the exact opposite by enabling all options which can be called using the "allnoconfig" or "defconfig", you can run the following command:

make defconfig
make

Once the compilation is complete, you now have Busybox binary which has all the available applets by default:

Enabling all applets, the Busybox binary still comes out to be less than 900k. If you wanted to create a custom Busybox with specific applets, you can manually edit the .config file which is where the features are either enabled or disabled. This can get very tedious, luckily there is a make option which allows for an interactive menu on selecting the applets you would like to include in the build.

To enable the interactive menu, you will run the following command:

make menuconfig

From here, you will be able to configure the Busybox settings and the various applet types by their functions such as networking or mail utilities. One feature that is actually disabled in the VMware's version of Busybox is the support for large files, if you tried to tar up a file that was larger than 2GB and then extract the file, you will notice you get an error regarding the file size. The reason is VMware decided to not enable this feature in their Busybox build.

Once you are done selecting or de-selecting all your Busybox settings and applets, you will need to save your configuration which is stored in the .config.

Once you have exited from the interactive Busybox menu, you are now ready to build your custom version of Busybox, you will run the following command:

make

If everything went well, you now should have a busybox binary in your current working directory. Here is an example of my custom Busybox image:

If you would like to customize the version information found when just running busybox command without any arguments, you can edit the Makefile and append your custom text to EXTRAVERSION variable.

Now you just need to re-run the "make" command and your new busybox binary will include the additional version information.

Now before you jump and start creating your own Busybox binary, I must throw in another caveat that re-iterates the title of this post. Just because you have Busybox built with all these applets, it does not mean it will run 100% on ESXi, the reason being is there are specific dependencies that the non-VMware Busybox applets may rely on which are just not available with ESXi. This is one of the reasons why VMware did not just enable all applets from Busybox to begin with, your mileage will vary depending on the particular command you have enabled.

Here is an example of my custom Busybox applet "crontab" using the "-l" flag which lists any active cron entries for the particular user:

It runs just fine on ESXi as you can see, but let's try using the "-e" flag which if you are familiar with using crontab you will know that is the option to edit your cron entries:

Ooops, what's this? It looks like this particular operation of crontab relies on vfork which is not implemented. I have seen other similar errors with other applets relying on particular dependencies in the environment that just does not exist with ESXi. I have not tested every single applet and some may work 100% while others may be partially functional, you will need to test and verify for yourself.

If you feel adventurous, go ahead and download Busybox and start playing with it. I would highly recommend that you test this in your vSphere development environment before trying this on a production host. I would also recommend that you do NOT replace the default Busybox binary found on ESX(i) as you can run into some serious issues. Since the Busybox binary is self-contained, you can store it in /tmp or somewhere more permanent such as a local or remote VMFS datastore and renaming the file will also remove any confusion.

If you find other utilities that you feel that should be included in the default Busybox applet and do not want to resort to something like Poor man's traceroute for ESXi, be sure to submit your feedback to either your VMware rep or file a feature request.

If you are interesting to learning more about Busybox, check out their FAQ page and this page for more details.

Again, another warning:
!!!! THIS IS NOT SUPPORTED BY VMWARE - PLEASE USE AT YOUR OWN RISK !!!!